title: Magnetic, high-field EPR studies and catalytic activity of Schiff base tetranuclear CuII2FeIII2 complexes obtained by direct synthesis.
abstract: Two novel heterometallic complexes [Cu2Fe2(HL(1))2(H2L(1))2]·10DMSO (1) and [Cu2Fe2(HL(2))2(H2L(2))2]·2DMF (2) have been prepared using the open-air reaction of copper powder, iron(II) chloride and DMSO (1) or DMF (2) solutions of the polydentate Schiff base (H4L(1), 1; H4L(2), 2) formed in situ from salicylaldehyde (1) or 5-bromo-salicylaldehyde (2) and tris(hydroxymethyl)aminomethane. Crystallographic analysis revealed that both compounds are based on the centrosymmetric tetranuclear core {Cu(II)2Fe(III)2(μ-O)6} where metal centres are joined by μ-O bridges from the deprotonated ligands forming a nonlinear chain-like arrangement. Variable-temperature (1.8-300 K) magnetic susceptibility measurements of 1 and 2 showed a decrease of the effective magnetic moment value at low temperature, indicative of antiferromagnetic coupling (JCu-Fe/hc = -10.2 cm(-1), JFe-Fe/hc = -10.5 cm(-1) in 1, JCu-Fe/hc = -10.5 cm(-1), JFe-Fe/hc = -8.93 cm(-1) in 2) between the magnetic centres in both compounds. They reveal an exceptionally high catalytic activity in the oxidation of cyclohexane with hydrogen peroxide under mild conditions, with the best observed yield/TON combined values of 36%/596 and 44%/1.1 × 10(3) for 1 and 2, respectively.
authors.affiliation: Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, The University of Lisbon, Avenida Rovisco Pais, 1049-001 Lisboa, Portugal. pombeiro@ist.utl.pt.
authors.forename: Oksana V
authors.initials: OV
authors.lastname: Nesterova
authors.forename: Eduard N
authors.initials: EN
authors.lastname: Chygorin
authors.forename: Vladimir N
authors.initials: VN
authors.lastname: Kokozay
authors.forename: Volodymyr V
authors.initials: VV
authors.lastname: Bon
authors.forename: Irina V
authors.initials: IV
authors.lastname: Omelchenko
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Shishkin
authors.forename: Ján
authors.initials: J
authors.lastname: Titiš
authors.forename: Roman
authors.initials: R
authors.lastname: Boča
authors.forename: Armando J L
authors.initials: AJ
authors.lastname: Pombeiro
authors.forename: Andrew
authors.initials: A
authors.lastname: Ozarowski